1. Field of the Invention
The present invention concerns a clutch mechanism for a friction clutch, in particular for a motor vehicle, and relates more particularly to a clutch mechanism equipped with a device for compensating for wear due notably to wear on the friction linings, the said device, hereinafter referred to as the wear take-up device, operating as the said linings wear.
2. Description of Related Art
The conventional friction clutch generally has a reaction plate, possibly in two parts in order to form a damping flywheel, fixed with respect to rotation to a first shaft, usually a driving shaft such as the crankshaft of the internal combustion engine, and supporting through its external periphery a cover to which at least one thrust plate is attached.
The thrust plate is fixed with respect to rotation to the cover and reaction plate whilst being able to move axially under the action of axially acting engagement means and controlled by disengagement means, generally having a metallic diaphragm bearing on the cover, whilst a friction disc, carrying friction linings at its external periphery, fixed with respect to rotation to a shaft, usually a driven shaft such as the input shaft of the gearbox, is interposed between the thrust plate and reaction plate so as to be clamped between them when the clutch is in the engagement position. The diaphragm controls the axial movement of the thrust plate when it is actuated by a clutch release bearing.
During the life of such a clutch, the friction linings, as well as the counter-materials, thrust plate and reaction plate, wear, which causes a variation in the position of the thrust plate and the positions of the axially acting elastic means and of the clutch release bearing, giving rise to a variation in the clamping force between the friction disc on the one hand and the thrust and reaction plates on the other hand, because of the changes in the working conditions of the diaphragm, and the force needed to declutch is affected thereby. By providing such a clutch with a wear take-up device, these drawbacks are avoided, the diaphragm, and the clutch release bearing, usually in constant abutment on the diaphragm, occupying the same position when the clutch is in the engagement position.
There has been proposed, notably in the French patent application FR-A-2 753 503 filed on Sep. 17, 1996 under the number 96 11297, a clutch mechanism for a friction clutch, in particular for a motor vehicle, of the type having a reaction plate intended to be fixed with respect to rotation to a driving shaft, a friction disc, carrying friction linings at its external periphery, intended to be fixed with respect to rotation to a driven shaft, the said mechanism comprising a thrust plate, a cover intended to be fixed to the reaction plate, engagement means, acting axially and controlled by disengagement means, acting between on the one hand the cover and on the other hand the thrust plate by means of abutment means, the thrust plate being fixed with respect to rotation to the cover whilst being able to move axially with respect to it and being subjected to the action of elastic return means returning the thrust plate axially towards the cover, the said mechanism also including a wear take-up device comprising ramp means having circumferentially disposed ramps, the said means being placed axially between the abutment means and the thrust plate, the said ramps being adapted to cooperate with counter-ramp means.
Naturally, the clutch being equipped with a wear take-up device, it is necessary, after it has fulfilled its function, to put it in its so-called zero position corresponding to linings in the new state, after changing the friction disc whose linings have been worn: means have already been provided for this operation to be easy to implement, as is for example described in the French patent application filed on May 30, 1997 under the number 97 06655.
It is advantageous for this operation also to be carried out on the clutch mechanism alone, consisting of the cover, engagement means, the wear take-up device and the thrust plate, constituted a subassembly, before mounting on the reaction plate or flywheel.
Such an operation is difficult when the engagement means, expanding, when the mechanism is in this storage position, in some way axially jam the ramp means against the thrust plate, itself held, with respect to the cover, by the return means or other axial stops.
The clutch mechanism being equipped with a wear take-up device, the engagement means almost always occupy, as explained above, the same working position with respect to the cover. This is taken advantage of by the present invention in order to limit the travel of the engagement means with respect to the cover.